|
Search: id:A109428
|
|
|
| A109428 |
|
Numbers n such that sigma(n)/omega(n) is not an integer [sigma(n) =sum of divisors of n; omega(n)=number of distinct prime factors of n]. |
|
+0
2
|
|
| 18, 36, 50, 72, 84, 98, 100, 144, 156, 162, 196, 200, 225, 228, 242, 252, 273, 288, 300, 324, 336, 338, 364, 372, 392, 399, 400, 441, 444, 468, 484, 516, 525, 532, 576, 578, 624, 648, 651, 676, 684, 700, 722, 732, 741, 756, 777, 784, 800, 804, 819, 868, 876
(list; graph; listen)
|
|
|
OFFSET
|
1,1
|
|
|
COMMENT
|
Integers greater than 1 and not in A109427.
|
|
EXAMPLE
|
The number 36 is in the sequence because sigma(36)=91 (1+2+3+4+6+9+12+18+36) and omega(36)=2 (2,3) and so sigma(36)/omega(36)=91/2.
The number 12 is not in the sequence because sigma(12)=28 (1+2+3+4+6+12) and omega(12)=2 (2,3) and so sigma(12)/omega(12)=14.
|
|
MAPLE
|
with(numtheory): b:=proc(n) if type(sigma(n)/nops(factorset(n)), integer)=false then n else fi end: seq(b(n), n=2..1000);
|
|
CROSSREFS
|
Cf. A109427.
Sequence in context: A160844 A040306 A073332 this_sequence A166403 A004941 A004961
Adjacent sequences: A109425 A109426 A109427 this_sequence A109429 A109430 A109431
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
Emeric Deutsch (deutsch(AT)duke.poly.edu), Jun 28 2005
|
|
|
Search completed in 0.002 seconds
|
